What Is Protein? And Why Is Protein Important?

Protein tends to get a lot of attention in conversations about health and weight management – and for good reason. So why is protein important?

It’s not just for athletes or gym-goers. Whether you’re trying to feel fuller between meals, support muscle health as you lose weight (including on GLP-1 weight loss treatments), or simply eat well, protein plays an important role in day-to-day health.

What Is Protein?

Protein is one of the three macronutrients we need in our diet, alongside carbohydrates and fats. Macronutrients provide energy and keep the body functioning normally. Protein supports growth, repair and maintenance of body tissues throughout life.

Protein is made up of smaller units called amino acids, often described as the ‘building blocks’ of protein.

There are 20 different amino acids in total. Some can be made by the body (non-essential amino acids). Others must come from the diet (essential amino acids). We get them by eating a varied diet that includes foods such as beans, lentils, nuts, seeds, vegetables, dairy products, fish and meat.

When we eat protein-containing foods, the body breaks them down into amino acids. It then rebuilds them into the specific proteins it needs – from muscle tissue and bones to enzymes, hormones and immune cells.

What Does Protein Do in the Body?

Protein is found in almost every cell of the body and plays a wide range of roles, including:

• Building and maintaining muscle, skin, hair, nails and connective tissue 
• Supporting immune function 
• Producing enzymes and many hormones 
• Helping to transport substances in the blood, such as haemoglobin, which carries oxygen 
• Contributing to energy intake when needed 

Protein and Muscle Health

One of the most well-known roles of protein is its involvement in muscle repair and maintenance. Muscle tissue is constantly being broken down and rebuilt. Protein provides the amino acids needed for this process, known as muscle protein synthesis.

Regular physical activity, particularly resistance or strength-based exercise, increases the body’s demand for protein.

Eating enough protein as part of a balanced diet helps support recovery and adaptation following exercise. The British Dietetic Association (BDA) recommends you distribute your protein intake evenly throughout the day.

Ideally eat protein every three to four hours to support muscle repair and muscle growth. While you can eat protein anytime within 24 hours after working out, doing so sooner tends to be more effective.

Protein, Fullness and Weight Management

You might often hear people talk about high-protein diets for weight management, and this isn’t just a trend. Compared with carbohydrates and fats, protein generally takes longer to digest. This can help you feel fuller after meals, which may make it easier to manage appetite throughout the day.

Digesting protein also requires slightly more energy than digesting carbohydrates or fats. Together, these effects may support weight management when protein is included as part of a balanced, enjoyable way of eating.

For some people – including those using GLP-1 medications – appetite may be reduced and meal sizes smaller. In these situations, prioritising protein at meals can help ensure nutritional needs are met despite eating less overall.

Protein can also help maintain muscle mass during weight loss, which is important for long-term health and strength. For more tips on how to prevent muscle loss while losing weight, check out this blog.

Protein and Blood Sugar Balance

Protein plays a role in how the body responds to meals. When eaten alongside carbohydrates, protein can slow the digestion and absorption of glucose into the bloodstream. This results in a more gradual rise in blood sugar levels compared with eating carbohydrates alone.

Maintaining stable blood sugar levels is important for everyone, not only for people with diagnosed blood sugar disorders. Hormonal changes across the lifespan, including menopause, may influence insulin sensitivity. Including a source of protein at meals and snacks may help support steadier energy levels throughout the day.

Disclaimer: Protein intake does not replace medical treatment for conditions such as diabetes. But balanced meals that include protein can form part of general healthy eating advice.

Protein and Bone Health

When thinking about bone health, nutrients such as calcium and vitamin D often come to mind. But protein also plays an important role. Protein makes up a significant portion of bone tissue and helps maintain bone structure.

Bone mass naturally declines with age, particularly during life stages such as menopause. This is reflected in the fact that around one in three women and one in five men over the age of 50 experience osteoporosis-related fractures worldwide.

It’s never too early or too late to support your bones. Eating a balanced, nutrient-rich diet and staying active keeps them strong and can reduce age-related bone loss. This is especially important during periods of weight loss, when overall nutrient intake may be lower.

So including protein-rich foods as part of a varied diet can contribute to long-term musculoskeletal health, supporting both bone strength and muscle maintenance.

Protein, Hormones and Immune Function

Many hormones and enzymes in the body are made from protein. While sex hormones themselves are not protein-based, their production and regulation rely on other protein-derived hormones and enzymes.

Protein is also essential for the immune system. Antibodies and immune cells are made from amino acids, and insufficient protein intake over time can impair immune responses. Protein-rich foods often provide additional nutrients, such as zinc, iron and B vitamins, which further support immune health.

How Much Protein Do We Need?

In the UK, the general recommendation for protein intake is around 0.75 grams per kilogram of body weight per day for adults.

This amount of protein is enough to meet the needs of most people. But some may benefit from a higher intake, including:

• People who are physically active or exercise regularly
• Older adults, as muscle mass naturally declines with age
• Individuals aiming to preserve muscle mass during weight loss

For GLP-1 patients, recommended intake is 1.2 to 1.5 grams of protein per kilogram of body weight.

Protein needs are influenced by body size, age and activity levels. Although average needs can differ between men and women, individual requirements vary.

If appetite is low – something some people experience during weight loss or while using GLP-1 medications – focusing on protein-rich foods and spreading intake across meals and snacks can help make meeting protein needs feel more manageable.

Most people can safely follow these recommendations. But individuals with rare metabolic conditions such as phenylketonuria (PKU) should consult a healthcare professional about their protein intake.

Does the Type of Protein Matter?

Including a variety of protein sources in your diet can help meet your protein needs. Both animal and plant proteins can contribute to overall intake. Examples of high-protein foods include:

• Meat and poultry
• Fish and seafood
• Eggs
• Dairy products, like Greek Yogurt
• Beans, lentils and chickpeas
• Nuts and seeds
• Wholegrains such as quinoa and oats

When you look at individual foods, animal-based proteins naturally contain all the essential amino acids the body needs. This is why they’re often called ‘complete’ proteins.

Many plant foods don’t contain all these amino acids in large amounts on their own. However, when you eat a variety of plant-based protein foods across the day – and you’re eating enough overall – your body can still get everything it needs.

Protein powders marketed to specific groups often contain added vitamins or minerals. But the protein itself is not fundamentally different.

Many powders can also be highly processed and may include added sugars, flavourings, or other ingredients. They can be useful occasionally, for example, to boost the protein content of a meal or recipe, or when you’re short on time. But whole foods should form the foundation of your protein intake whenever possible.

Practical Tips For Including Protein in Your Day

• Aim to include a source of protein at each meal.
• Spread protein intake evenly across the day, roughly every three to four hours.
• Combine protein with carbohydrates and fats for balanced meals.

Key Takeaways

• Protein is essential for overall health: It supports muscle, bone, skin, hair, nails, hormones, enzymes, and the immune system. 
• Spread protein intake throughout the day: Including protein at each meal or snack helps maintain muscle repair. It supports recovery from exercise and may help with appetite control.
• Include a variety of protein sources: Both animal and plant proteins contribute to your needs. Eating a mix of protein foods across the day ensures you get all essential amino acids.
• Whole foods are best: Protein shakes and powders can be useful to have on hand for occasional use. But whole foods provide additional nutrients and are less processed, making them a better foundation for your diet. 
• Protein matters at every life stage: Adequate protein supports bone health. It helps maintain muscle during aging or weight loss, and can assist with blood sugar stability. This makes it important for everyone, from young adults to older adults. 

References

www.osteoporosis.foundation. (n.d.). Epidemiology | International Osteoporosis Foundation. [online] Available at: https://www.osteoporosis.foundation/health-professionals/fragility-fractures/epidemiology.

‌BDA (2020). Sport and exercise. [online] www.bda.uk.com. Available at: https://www.bda.uk.com/resource/sport-exercise-nutrition.html.

SACN (2021). SACN statement on nutrition and older adults living in the community- statement-on-nutrition-and-older-adults-living-in-the-community 2. [online] Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/953911/SACN_Nutrition_and_older_adults.pdf.

Spreckley, M., Ruggiero, Cara F. and Brown, A. (2026). Nutrition Strategies for Next‐Generation Incretin Therapies: A Systematic Scoping Review of the Current Evidence. Obesity Reviews. doi:https://doi.org/10.1111/obr.70079.

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